Tapping question

Gents,

I am making a Stuart Triple Expansion engine, or at least giving it my best shot. According to the drawings, I have to tap a hole 7 BA “dead”. Can anyone tell ne what “dead” means in this context?

Thanks,

Mark

I think you will find they are actually plain holes in the valve gear that need to be drilled through so they have minimal clearance on the shanks of the 7BA threaded pivots so you don't get excess play in the linkages.

The other 7BA CL (clearance) holes tend to have a bit more wiggle room.

If you have a 3/32" reamer or a 2.5mm if metrically minded then you could ream the "dead" holes and make the pivots to suit, 7BA will thread onto either of those with no problem and the nuts only stop the pivot pins coming out.

Edited By JasonB on 25/04/2023 11:54:14

+1 for what Jason says but best to measure the actual shank size if you plan to use 7BA bolts as pivots.

There was always enough variation in actual shank sizes of the smaller BA bolts to make the difference between too snug, just right, and a bit too loose depending on supplier, purpose or, usually in my case, what I scavenged it out of when reducing a broken thing to useful parts. Presumably due to effects of anti corrosion plating or the lack of it. I had pack of some small bare steel BA bolts through my hands that I could easily be convinced were actually made undersize to allow for the, very thin, chromate or other anti corrosion measures. The difference being completely irrelevant for all normal purposes.

In these small sizes you need to test drill to verify the size of hole your drill actually produces. Slight oversize is common, even if it the drill is brand new, and likely if it's a used one. Which could be a good thing because such oversize from basically decent, but miles-on-the-clock, drill may well be just enough oversize to make a nice pivot bearing. Letter and number drills tend to be useful hear because of the very small size increments, especially at the small to mid end of the number range.

Clive

Ok thanks Jason and Clive, I will do my best. It’s great knowing you can come here and get such help and at such very short notice.

Thanks again,

Mark